Collected blood may be conventionally centrifuged to remove the plasma and the buffy coat layer, leaving behind the "packed red cells," as the mass of red cells is substantially separated from the plasma. This is desirable for several reasons, first to collect the plasma for separate therapeutic use, but also because it is desirable to administer concentrated red cells during major surgery, to provide the patient with a maximum amount of red cells with a minimum of added fluids, to avoid overburdening the patient's vascular system with excess fluids.
Accordingly, it is deemed desirable in many forms of medical practice and blood banking to store the packed red cells separately, apart from a substantial portion of the plasma, for later administration to a patient during major surgery or the like, while the collected plasma finds a separate medical use, for example administration to another patient or processing into various medical components such as antihemophilic factor, and plasma protein fraction.
In the long term storage of blood, it has been previously reported that a unit of packed red cells may be admixed with about 100 ml. of blood plasma, which is far less than normal blood, or preferably, the packed cells can be reconstituted with about 100 ml. of a solution known as SAG, comprising salt (sodium chloride) adenine, and glucose. The term "unit" of blood or packed red cells as used herein is as commonly used in blood banking circles, comprising the amount of red cells in a standard single collection of blood (typically, 225 ml. of packed cells, but of course subject to variation according to the individual donor). See for example the article by Lovric, et al., Medical Journal of Australia 1977, 2: 183-186.
The packed cells which are reconstituted with SAG solution have been shown to be storable for 35 days with improved viability of the red cells, when compared with packed red cells stored in a similar amount of plasma.
It has also been suggested to use mannitol, which is a type of sugar, as a reagent to improve the viability of stored blood cells. However, surprisingly, it has been found in accordance with this invention that despite the fact that SAG solution contains abundant sugar already, the addition of mannitol provides a significant improvement in the viability of packed red cells stored in contact therewith. Accordingly, longer storage times appear to be possible for packed red cells with better viability than has been previously available.